I kindly pointed out to this eBay seller that his tank was indeed not for a 500 or 550, but in fact looked like a 69-76 CB750 tank.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=4559662448He responded:
"The CB500/CB550 has the fuel valve on the left side.This is on the left side.The CB750 69-76 SOHC has the fuel valve on the Right Side.I own a 69 CB750 Sandcast and 74 CB750.I have been collicting CB750s for over 30 years.This is not a CB750 fuel tank.Please do you research if your looking for a CB500/CB550 tank."
I'm not trying to get into a pissing contest with the guy, but rather trying to keep an uninformed buyer from being dissapointed, and perhaps making it easier for this guy to sell his tank.
Can someone tell me what years the 750 had the petcock on the left or right side? I myself have a 750 tank of this style with the petcock on the right. Were any made in this style with the petcock on the left?